A hybrid electric vehicle implements operating modes, such as an EV mode in which it is driven only by a motor, an HEV mode in which it simultaneously uses an engine and a motor, and an engine mode in which it uses only an engine, according to the combination of the engine and the motor. It is possible to maximize system efficiency and improve fuel efficiency according to the combination of the operating modes.
An Electrically Variable Transmission (EVT) may be an electric CVT that includes one or more planetary gear trains and two motor/generators to have continuously variable transmission function as in a Continuously Variable Transmission (CVT).
The EVT is controllable such that an engine may be operated at an optimally efficient operating point. Therefore, the EVT has a great advantage of making the most efficient use of engine energy by splitting power input from the engine into a motor/generator as an electric part and an output shaft as a mechanical part through a planetary gear train according to the control of the EVT.
However, a one-mode EVT widely applied in recent years has a disadvantage of increasing vehicle costs since there is a need for a high-capacity motor/generator due to transmission of high power to an electric part at the time of initial starting or in a high-speed section.
To overcome this disadvantage, there is proposed a two-mode EVT structure using two motor/generators.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.